1. Field of the Invention
The present invention relates to data communication, equipment, and, more particularly, to a communication system involving simultaneous voice and data modems.
2. Description of the Related Art
The growth of the personal computer industry is attributable in part to the availability of inexpensive, yet powerful computers. Improvements in processor, memory, data storage and communications technologies have resulted in computers which can provide sufficient processing capability for audio visual applications such as computer-aided design, three-dimensional animation, and multimedia presentation for extended durations, even when users are at remote or relatively inaccessible locations.
The communication of digital information such as data over analog transmission links such as telephone lines and trunks is known in the art. At the transmitting end of the link, a modem uses a representation of the digital information to modulate a carrier frequency and transmits the modulated carrier frequency on the transmission link. At the receiving end of the link, another modem demodulates the carrier frequency to retrieve the representation of the digital information, and reconstitutes the digital information therefrom. A pair of modems can thus engage in a communication protocol that includes control and signalling to set up and terminate the communication connection.
The continuing development of computer and telephone communication systems requiring expanded data conversion and processing capabilities, however, is taxing the transmission capability of existing telephone networks in that separate lines are required for computer communications and for human conversations. To reduce this load, voice and data modems recently appeared which allow a voice communication channel to be carried out simultaneously with a data communication channel such that both channels appear as a single communication to the transmission facility that interconnects the modems. Simultaneous voice and modem data transmitted over the same communications link between two sites has been accomplished in several ways. The most common communications links between two sites is the telephone line. The most common data handling equipment to communicate over a communications link is the computer modem which modulates digital data onto a carrier for transmission in the voice band of a telephone line. A wide variety of modulations standards promulgated by such international groups as ITU for communications in the voice band exist. In these schemes, the voice channel is typically created by modulating a second carrier frequency with the representation of the voice signals. Alternatively, a digital implementation of the voice and data modem allows voice signals to be encoded in digital form and the encoded voice and data are multiplexed for transmission to the other side.
Currently, one simultaneous voice over data standard known as digital simultaneous voice and data (DSVD) is standardized in an International Telecommunication Union specification ITU-T Recommendation V.70. DSVD improves upon other simultaneous voice and data technologies by allocating bandwidth to both jobs with the ability to simultaneously support voice transmission at 9.6 kilobauds per second on a standard telephone line while the remaining bandwidth is available for data transmission. Thus, by providing the ability for a single point-to-point connection to share user data and exchange voice at the same time, DSVD allows the simultaneous exchange of data and digitally encoded voice signals over a single dial-up phone line. The voice quality is essentially the same as that provided over present phone lines. DSVD modems use V.34 modulation which provides up to 33.6 kilobits per second.
The arrival of the wide range of modems conforming to the DSVD standard eliminates in many cases the need for two separate phone lines (one for voice, and one for data) when using collaborative applications such as desktop personal conferencing or interactive games. However, with the increasing number of organizations located in multiple sites, effective group working requires communications facilities that can join together more than two locations. Multi-point communications provides such a facility for both audiovisual and data communications, overcoming current point-to-point network constraints. The need for multiple DSVD connections is essential when multiple users need to share the data and exchange voice simultaneously over the same link. However, present day DSVD solutions do not support such multiple DSVD connection. Thus, a need exists for low cost sharing of data and the exchange of voice information at end-user premises.